There is a significant need in the art for improved secondary (rechargeable) batteries having high energy density, decreased cost, improved safety, reduced thermal management and improved stability of component supply. Batteries having such improved characteristics will be useful in a variety of applications and are of particular interest for electric utility grid storage.
Electric utilities are seeking more cost effective and efficient strategies to manage energy delivery to the grid. Peak demand is frequently met by the use of relatively expensive gas turbines, which at times of low demand remain idle. Ideally, base load electrical energy production could be operated at optimum peak efficiency, with demand variations being either absorbed or delivered using some form of energy storage. Pumped hydro (PH) technology, where water is reversibly pumped from a lower to higher elevation, has been employed for such energy storage, where round-trip efficiency is typically 68%. However, acceptable sites for implementation of PH energy storage, based upon location and environmental concerns, are now very limited. An alternatively is the use of large storage batteries, where round-trip energy conversion efficiencies can exceed that of PH, and wherein siting is not limited by geography. The market for storage batteries for this application is expected to grow, provided that battery costs are reduced and performance is increased. Major issues that are currently limiting implementation of advanced battery systems for grid storage include: overall cost for materials and associated hardware, long-term availability of materials, safety, achieving long cycle life and 5) thermal management during operation. The present invention provides an improved battery to meet these requirements. The batteries of the invention incorporate no toxic materials, and are generally safer than comparable battery systems (e.g., sodium-sulfur systems).
Improved secondary batteries will also provide particular benefit for applications to electric vehicles and their use will translate into greater range for such vehicles.
U.S. Pat. No. 3,988,163 relates to a secondary battery having a molten sodium negative reactant, a sulfur and mixture of metal halides positive reactant melt, a carbon powder dispersed within the positive reactant melt, a solid member separating the negative reactant and the positive reactant, and a molten electrolyte on the positive reactant side of the solid member which is said to comprise a molten sodium haloaluminate. The solid member is said to be selectively-ionically conductive to sodium cations. The positive reactant is said to comprise molten sulfur and a molten mixture of metal halides. The metal halides are required to be “soluble to some extent in the sodium haloaluminate electrolyte of the battery”. Molten sodium haloaluminate is defined as “materials which include sodium halides, as for example, chlorides, bromides, fluorides, or iodides or sodium, and aluminum halides, for example, chlorides, bromides, fluorides or iodides of aluminum. Preferred metal halides are said to be aluminum chloride and antimony chloride. The positive reactant compartment of the battery is described as containing “electrolyte-sulfur mixture of metal halides positive reactant melt” and, more specifically as “sodium chloroaluminate-sulfur, aluminum chloride and antimony chloride melt. The battery is reported to operate at temperatures ranging from 150 to 225° C.
U.S. Pat. No. 3,877,984 relates to a secondary battery having a molten alkali metal negative reactant. a metal chloride positive reactant, a molten alkali metal chloraluminate electrolyte and a selectively-ionically-conductive separator positioned between the negative and the positive reactants. Metal chloride, sodium chloride and aluminum trichloride are combined in the positive reactant chamber and heat to form a melt. Exemplified metal chloride positive reactants included antimony chloride, ferric chloride and cupric chloride. The battery is reported to operate at temperatures ranging from 180 to 200° C.
U.S. Pat. No. 4,452,777 relates to an electrochemical cell having a sodium anode assembly, an alkali metal aluminum tetrahalide electrolyte where the cathode material is a transition metal chalcogenide or a reaction product of the chalcogenide with the electrolyte. The cathode material is described as being dispersed on a substrate which is inert under cell operating conditions. Exemplary substrates are carbon felt and nickel mesh. The preferred transition metal chalcogenide is reported to be VS2. Exemplary cells are reported to be operated at 165° C. or 170° C.
U.S. Pat. No. 5,476,733 reports a high temperature (200-400° C.) rechargeable electrochemical power storage cell where the anode compartment contains sodium active anode material, and the cathode compartment contains a sodium aluminum chloride molten salt electrolyte and a solid cathode comprising an electrolyte permeable porous matrix impregnated with the molten salt electrolyte which has solid active cathode material dispersed therein. The cell is operated at a temperature where sodium and the molten salt electrolyte are molten. The electrolyte is described as “a substantially equimolar mixture of sodium chloride and aluminium chloride in which the proportion of aluminium chloride in all states of charge is at most 50% on a molar basis.” The active cathode material is described as comprising at least one transition metal selected from the group consisting of Fe, Ni, Cr, Co, Mn, Cu and Mo having, dispersed therein, at least one additive element. In the description and the examples, the at least one additive element is said to be selected from the group consisting of As and Sb where the atomic ratio of transition metal to additive element in the active cathode material being 90:1-30:70. Only in the Abstract is the additive element said to be selected from the group consisting of As, Bi, Sb, Se and Te. The cathode is further described as “may contain, in addition, 2-12% by mass, based on the charged active cathode material, of sodium fluoride dopant and/or a sulfur-containing dopant whose sulfur forms 0.3-5% of the charged active cathode material by mass.”
U.S. Pat. No. 8,343,661 reports a rechargeable electrochemical cell having a cathode composition comprising certain transition metals, alkali halometallate, alkali halide, a source of Zn and a source of chalcogenide. The source of Zn and that of chalcogenide is reported to may be effective to improve the extractive capacity of the cell and to decrease cell resistance. Operating temperatures for the cell are reported to range from 200 to 500° C.
While electrochemical cells employing cathode materials which comprise chalcogenides have been reported, there remains a significant need in the art for electrochemical cells, particularly those that are rechargeable, which exhibit properties useful in a given application, such as useful levels of charge capacity and useful levels of energy density, which can be operated at practically useful temperatures, and which have enhanced safety and decreased cost. The present invention provides such electrochemical cells.